Lines from line chart are conecting the last and first points of data.

[venturafabiano]

Hello, guys!

I'm from Brazil. The X axis represents the months and the Y axis represents the volume.

I don't know why, but thelines are conecting the infos from january to december (or the other way around) with a line, as you can see below.  

Did it ever happened to some of you?

Loking forward for some help.

Many thanks,